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The Science of Pain

According to Aristotle, we have five senses – sight, smell, touch, hearing and taste. Pain is not one of them. Check out the link in the comments to see where Aristotle missed a few.

Pain is a feeling – an *experience* – but not a sensation. It sounds like semantics and although the difference may seem a little pedantic, the difference is important to understand if we’re trying to help clients living with pain.

We feel pain in a similar way to how we feel love; it comes from within us. We do not “feel” love as a sensation, but we feel “in-love”. There is of course a sensory component to pain – extremes of hot or cold, structural damage to tissue and chemical inflammation – which activate receptors in the skin to provide the nervous system and brain with information to make sense of what’s happening. But here’s the difference; a burning hot object does not create a ‘pain signal’; a noxious signal is sent to the brain as a warning of impending harm. The brain interprets the noxious signal and decides whether it will create an experience of pain, which in this case would invariably cause a protective behavioural response of withdrawal. We cannot “feel” pain on our skin. Through the skin we “feel” heat, cold and pressure but not pain. Touch is an input; pain in an output.

When we’re in-love, our thoughts can have profound effects on our behaviour and physiology; a racing heart and choosing to do things which we wouldn’t ordinarily consider. The experience of being in love can be overwhelming. A hug can be one of the most wonderful experiences, but if the pressure of an embrace increases, that pressure could quickly change from being warm, gentle and comforting to a painful, crushing, terrifying encounter that could quite literally squeeze the life out of us. The only thing that changed was the pressure. The sensation and meaning behind it is an output of your brain and nervous system; from “I like this, we should do it more often” to “oh my god I’m going to die”.

Free nerve endings create ‘nociception’, which may or may not be noxious. A warm hug creates a barrage of nociceptive input – the pressure, the temperature, the sensation of texture of clothing and skin. In the context and meaning of a hug with someone non-threatening, the hug has a meaning which is safe and enjoyable – our brain doesn’t normally equal a hug with danger. If the intent was to hug someone to death with increasing force, it would quickly take on a difference meaning and the sensory output would change dramatically. No doubt pain would likely become a factor, especially when ribs start to snap. The same can be said of heat – place your hand on a stove and turn it on and at some point, the nociceptive input from the sensation of ‘heat’ will become a painful experience to drive subsequent behaviour.

Pain is a normal and natural biological mechanism designed to protect the body from harm. Nociceptive pain is associated with a noxious stimulus from thermal (too hot, too cold), chemical (inflammatory) and structural (actual or potential tissue damage) changes and afferent sensory input. Some people don’t experience this and typically they don’t survive beyond their 30s as a result – nature’s alarm system is vital.

Some people have a greatly exaggerated experience of pain called hyperalgesia. Some people experience pain with sensations which would not normally be painful, for example simply having clothing or bedding touching skin, called allodynia.

Disease states aside, in the absence of nociceptive pain i.e. there being no good reason for it, something about the nervous system is typically creating an inappropriate output. In this instance it would be biologically unhelpful. A gallstone pushing its way through a ureter is extremely pain but not damaging – it’s not supposed to be there and needs to be removed. The stretch of a full bladder can be painful – it needs to be emptied. Cancer can be painful – that needs to be treated. Food poisoning, a twisted bowel, dehydration – all helpful forms of pain which should trigger us to act accordingly. Depending on the cause, various medications can help reduce pain (whether unhelpful or not), from simple paracetamol and ibuprofen to strong opioids.

Unhelpful pain is unfortunately common. It is not a problem with a body part, state of disease or injury – it’s a problem with the alarm system itself. When pain is unhelpful, the treatment focuses on the alarm system, not the tissues. Anti-depressants and anti-epileptic medications are sometimes the drug of choice when the goal is to turn down the sensitivity of the alarm system because those medication act on the brain and nervous system. They act to change the output, not the input.

This is a crude summary of an extremely complex topic – pain.

If you’re experiencing pain and unsure why, or want some help turning it down or needing strategies to work with it, we would like to help you.